1. Field of the Invention
The present invention relates generally to means for connecting microelectronic devices and systems. More particularly, the invention relates to improved flex-circuit based interconnect solutions for electronic circuits.
2. Description of Related Art
The evolution of smaller, lighter electronic devices with ever-increasing functionalities has increased the need for interconnection methods that can handle the flow of large amounts of data between various circuits or modules in a device. Flex circuits are often used to provide a signal routing means that can be easily located in confined places within an equipment enclosure. They are also used to maintain electrical connections between two components that must move relative to one another; examples are the connections between the motherboard and the display on a laptop computer, or in many cell phones.
Various approaches have been used to enable a long, flexible circuit to be reliably connected to a component such as a motherboard. In one case, a socket is permanently installed on the motherboard (typically by soldering). A mating plug is affixed to the end of the flex by mechanically clamping or crimping; this plug contains internal metal pins that pierce the flex to complete an electrical connection between the lines on the flex and the contacts on the plug that will mate with corresponding contacts on the socket. As the number of lines increases, and the pitch becomes correspondingly smaller, both the cost and reliability of this approach can suffer.
Another approach, used particularly when the flex connection might need to withstand especially demanding mechanical forces, is to affix rigid circuit boards on both sides of the flex near the terminations. These boards typically have metal plated through holes and can be placed flat against the motherboard to secure a strong soldered connection. Connectors may also be further strengthened by potting in epoxy.
Another approach, used particularly for the assembly of flex circuits to Liquid Crystal Displays (LCD), is to bond the closely spaced finger contacts disposed at the edge of the flex circuits directly to similarly spaced pads of the glass display using either liquid or film Anisotropic Conductive Adhesives (ACA). Small conductive particles randomly distributed in the ACA material enable electrical contact to be established between the finger contacts of the flex circuit and the pads of the LCD display through the vertical (Z-axis) direction but not laterally between adjacent pads do to their small size and low particle loading (typically 5-8% by volume) within the adhesive. These bonds are intended to be permanent and are therefore not easily removed.